Mechanical and chemical-mechanical planarization processes (collectively “CMP”) remove material from the surface of micro-device workpieces in the production of microelectronic devices and other products. FIG. 1 schematically illustrates a rotary CMP machine 10 with a platen 20, a carrier head 30, and a planarizing pad 40. The CMP machine 10 may also have an under-pad 25 between an upper surface 22 of the platen 20 and a lower surface of the planarizing pad 40. A drive assembly 26 rotates the platen 20 (indicated by arrow F) and/or reciprocates the platen 20 back and forth (indicated by arrow G). Since the planarizing pad 40 is attached to the under-pad 25, the planarizing pad 40 moves with the platen 20 during planarization.
The carrier head 30 has a lower surface 32 to which a micro-device workpiece 12 may be attached, or the workpiece 12 may be attached to a resilient pad 34 under the lower surface 32. The carrier head 30 may be a weighted, free-floating wafer carrier, or an actuator assembly 36 may be attached to the carrier head 30 to impart rotational motion to the micro-device workpiece 12 (indicated by arrow J) and/or reciprocate the workpiece 12 back and forth (indicated by arrow I).
The planarizing pad 40 arid a planarizing solution 44 define a planarizing medium that mechanically and/or chemically-mechanically removes material from the surface of the micro-device workpiece 12. The planarizing solution 44 may be a conventional CMP slurry with abrasive particles and chemicals that etch and/or oxidize the surface of the micro-device workpiece 12, or the planarizing solution 44 may be a “clean” nonabrasive planarizing solution without abrasive particles.
In most CMP applications, abrasive slurries with abrasive particles are used on nonabrasive polishing pads, and clean nonabrasive solutions without abrasive particles are used on fixed-abrasive polishing pads.
To planarize the micro-device workpiece 12 with the CMP machine 10, the carrier head 30 presses the workpiece 12 face-down against the planarizing pad 40. More specifically, the carrier head 30 generally presses the micro-device workpiece 12 against the planarizing solution 44 on a planarizing surface 42 of the planarizing pad 40, and the platen 20 and/or the carrier head 30 moves to rub the workpiece 12 against the planarizing surface 42. As the micro-device workpiece 12 rubs against the planarizing surface 42, the planarizing medium removes material from the face of the workpiece 12.
The CMP process must consistently and accurately produce a uniformly planar surface on the micro-device workpiece 12 to enable precise fabrication of circuits and photo-patterns. One problem with conventional CMP methods is that the planarizing surface 42 of the planarizing pad 40 can wear unevenly, causing the pad 40 to have a non-planar planarizing surface 42. Another concern is that the surface texture of the planarizing pad 40 may not change uniformly over time. Still another problem with CMP processing is that the planarizing surface 42 can become glazed with accumulations of planarizing solution 44, material removed from the micro-device workpiece 12, and/or material from the planarizing pad 40.
To restore the planarizing characteristics of the planarizing pad 40, the accumulations of waste matter are typically removed by conditioning the planarizing pad 40. Conditioning involves delivering a conditioning solution to the planarizing surface 42 of the planarizing pad 40 and moving a conditioner 50 across the pad 40. The conventional conditioner 50 includes an abrasive end effector 51 generally embedded with diamond particles and a separate actuator 55 coupled to the end effector 51 to move it rotationally, laterally, and/or axially, as indicated by arrows A, B, and C, respectively. The typical end effector 51 removes a thin layer of the planarizing pad material along with the waste matter, thereby forming a more planar, clean planarizing surface 42 on the planarizing pad 40.
One concern with conventional CMP methods is the difficulty of accurately measuring characteristics of the planarizing pad, such as pad thickness, contour, and texture. Conventional devices for measuring characteristics of the pad include contact devices and noncontact devices. Contact devices, such as probes and stylets, physically measure the planarizing pad. Contact devices, however, are inaccurate and are limited by their diameter. In addition, contact devices are limited by their ability to be used during a planarizing cycle. Noncontact devices, such as optical systems, are also inaccurate when used in-situ because the liquid medium on the planarizing pad distorts or obscures the measurements. In addition, many of these devices cannot be used in-situ because of their size. Accordingly, there is a need for a system that accurately measures the characteristics of a planarizing pad during and/or between planarizing cycles or conditioning cycles in-situ.